After finally getting the darned thing apart, and printing a new outer housing, I went about re-assembling the whole mechanism. This time, I tried to take care to make the future disassembly less painful.
To start with, I filed down the problematic outer bearing interfaces of the sun gear holder so that the bearings were a slip fit over them. These two interfaces don’t need to be particularly snug, so that was easy enough, if monotonous, to accomplish. I also machined out a some pockets around the magnet hole, to make it possible to just hot-glue the position magnet in place and more easily extract it.
Next, I re-installed the sun gear holder back in the rotor.
After that, I pressed the input bearing into the new planet input:
Then I went about installing the shaft output bearing into the planet output, the planet output into the output bearing, the planet shafts into the planet output, the planet bushings into the planets, and the planet bearings into the bushings.
Those got dropped onto the shafts, and the planet input was stuck into place.
After that, the screws were installed in the planet input, and the stator was fit onto the front housing, using a shrink fit again:
At this point, I aligned the rotor and pressed it and the primary shaft into place.
Now I used my paper strip alignment technique to get the rotor properly (or at least functionally) spaced from the stator.
At this point, the rotor still didn’t spin freely. Because of all the rework I’ve done, and my sloppiness in executing it, bits of the exploded bearings and other detritus had lodged themselves against the rotor and stator. The problematic pieces were small, sub 5 thousandths, but still plenty enough to cause the rotor to hang when spinning. These I carefully extracted under a microscope with a pair of tweezers.
At this point, I had a gearbox that spun freely and seemed mostly correct!
2 thoughts on “Rebuild of gearbox assembly”
Just realized you’re using a slightly different sun gear than Ben. Still using the same planet gears? If so, where did you source them? 40T 0.5 module gears with 8mm bores are surprisingly hard to find sources for (aside from Misumi).
Most of my gearboxes have slightly different gears than what Ben used, although I have one with a slight variant of the Misumi gear he used because I bought out SDP-SI and had them lying around. https://github.com/mjbots/moteus/blob/master/hw/be8108_gearbox/bom.txt has what most of mine are using.
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